Furnace for burning semi-liquid fuels



Oct. 1, 1957 H. c. L. MILLER L 2,808,011

FURNACE FOR BURNING SEMI-LIQUID FUELS v Filed Aug. 21, 1952 W W ,d

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INVENTORS HENRY O. L. MILLER HARRY A. RADDIN United States Patent FURNACE FOR BURNING SEMI-LIQUID FUELS Henry C. L. Miller and Harry A. Raddin, Richmond, Va., assignors to Miller Holft, Inc., Richmond, Va., a cor poratiou of Delaware Application August 21, 1952, Serial No. 305,648

1 Claim. (Cl. 110-7) It is an object of this invention to provide a method and means for burning semi-liquid fuels of relatively low heat content.

It is a further object of this invention to provide a method and means as aforesaid whereby the escape of solids from the furnace will be minimized.

The above and other objects will be made clear from the following detailed description taken in connection with the annexed drawings, in which:

Figurel is a vertical cross-section through one form of the improved apparatus; and

Figure 2 is a section on the line 22 of Figure 1.

This invention will be described with particular reference to the burning of black liquor resulting from the production of pulp by the semichemical or by the neutral sulphite type of cook. Either of such liquors represents a more difiicult burning problem than is presented by the black liquors from the normal kraft or soda cook. The invention, however, is applicable to all of the black liquors.

In the ordinary kraft or soda cook, yield of pulp ranges from 50-60 percent of the bonedry weight of the original chips and the black liquors therefor contain as complex lignin materials from 40-50 percent of the bonedry weight of the chips.

The solids therefore in the black liquor have a very substantial fuel value. When, however, the chips are cooked by the semi-chemical or neutral sulphite process the pulp yield runs from 75-80 percent, which means that in the black liquor solids there is only from 2025 percent of the original chips. Hence the fuel value is very much lower and the recoverable chemicals in the black liquor solids is in far higher proportion to total solids than in ordinary kraft or soda black liquors. With this high proportion of inorganic recoverable chemicals to organic combustible matter it becomes of the utmost importance to minimize the passage of any solids into the stack since any solids going to the stack necessarily will represent a higher percentage of recoverable chemicals.

The present invention contemplates a combustion chamber in the form of a cylinder with its axis vertical. While for most purposes a circular horizontal cross-section is preferred; for some purposes, the horizontal cross-section may be polygonal. In any case the cross-section should be uniform for a height at least approximately twice the mean diameter of the chamber. The top or outlet is substantially restricted in diameter and the bottom preferably is frusto-conical.

Tangential air jets are provided at three different levels to create and maintain a vortex which will heat fine particles adjacent the periphery of the combustion chamber, thus preventing them from emerging through the restricted outlet. Concentrated liquor is sprayed into the combustion chamber and against the chamber wall. The spray is preferably thin and is flattened in the vertical plane. The spray nozzle or a series of nozzles preferably is oscillated horizontally in order to deposit the liquor on a maximum portion of the combustion chamber wall. As the liquor is sprayed in at a concentration of from 2 50-70 percent solids and strikes the hot combustion wall it immediately sticks there and is thereby exposed to the heat of the combustion chamber. As the heat of the combustion chamber evaporates the moisture of the liquor, chunks are formed which detach themselves from the wall and drop to the lower frusto-conical section. The air supply is adjusted so that Within the lower section the organic material burns primarily to carbon monoxide, thus maintaining a reducing atmosphere in which the inorganic material melts to form a smelt which drops through an outlet into a dissolving tank. Additional air is supplied adjacent the liquor spray and adjacent the top of the combustion chamber in order to burn the carbon monoxide formed at the bottomof the chamber completely to carbon dioxide and to assist, at three levels, in

maintaining the circular motion of the combustion gases.

Within the chamber, due to the tangential jets, there is maintained a high circular velocity but there is only a very modest velocity in the vertical direction through the outlet.

It will be recognized that the foregoing represents an adaptation of some of the principles of our copending application Serial No. 152,294, filed March 28, 1950, now Patent No. 2,614,513.

Referring now to Figure 1 there is shown a cylindrical shell 10, a frusto-conical lower portion 12 and an upper gas outlet 14. A lower slag outlet 16 is provided at the bottom of the frusto-conical portion and through this outlet 16 molten chemicals are removed. iust above the outlet 16 are one or more tangential air jets 18 through which roughly 30 percent of total air is supplied. Clearly enough this will maintain a reducing atmosphere within the frusto-conical portion so that the burning in this section will be to carbon monoxide.

Approximately midway of the height of the cylindrical shell 10 there are one or more additional tangential air jets 20 and within this area the spray or sprays 22 of concentrated black liquor is introduced. Other air jets 24 are directed tangentially adjacent and slightly below the annular constriction 26 which defines the gas outlet 14.

The furnace is started and brought up to heat by any conventional means such, for example, as an oil burner 19. Concentrated black liquor is then introduced through the nozzle 22 in the form of a flat spray which expands along the lines 28 and impinges on the wall of the chamber 10. The air jets 20 are similarly expanded to create a vortex vertically coextensive with the area of the wall 10 receiving liquor from the nozzle 22. Approximately 50 percent total air is supplied in this area with the remainder supplied by the jets 24. It will be clear that with enforced swirling of the gases throughout the chamber 10 and with only a moderate central vertical velocity, it will be almost impossible for any solid particle, however fine, to emerge through the gas outlet 14. All solids therefore ultimately must find their way to the bottom where, if organic, they are burned and, if inorganic, they are smelted.

For some purposes the nozzle or nozzles 22 should be oscillated horizontally toward and from a tangential position while for other purposes it will be more effective to oscillate the nozzles on each side of a radial median position. In either case the spray emerging from the nozzle should be flattened in a vertical plane. Also, in either case, the vortex created by the air jets 20 will distort the liquor jet emerging from nozzle 22, extending the area of the chanrber wall covered by the jet in the direction of the vortex, while shortening the area covered by the jet in the direction opposite the vortex. Only the liquor jets oscillate. The air jets, while in substantially the same horizontal plane as the liquor jets, are fixed within that plane.

We claim:

A method of operating a substantially cylindrical com- Patented Oct. 1, 1957- 3 4i bustion chamber having its axis vertical and having a re- References Cited in the file of this patent stricted outlet for combustion products in its top surface UNITED STATES PATENTS comprising: introducing tangentially, approximately midway between top and bottom of the chamber, a jet of a 901,232 Eldred 1908 water slurry containing burnable and unburnable solids; 5 1530321 Pollock 1925 igniting and burning the burnable portion of saidv solids; 1779537 4 1930 introducing combustion air in a tangential jet in the same 2138278 1938 direction and in the plane of said slurry jet; introducing 2'161'110 Tofnlmson June 1939 additional combustion air in similar jets similarly directed 2357301 Bafley Sept 1944 adjacent the top and bottom of said chamber; allocating 10 2362066 Hales. 1944 the total air among the several jets to supply approximate- 2385'955 Tomhnson 1945 ly 50% of the air to the jets adjacent the slurry jet, 2535730 Gadet 1950 approximately 30% to the jet adjacent the bottom of the FOREIGN PATENTS chamber and the balance to the jet adjacent the top of the 305,270 Great Britain Feb 1, 1929 chamber; introducing all of said ets at a velocity such 10 117,071 Switzerland Aug 20, 1946 as to create and maintain a vortex which will heat fine particles adjacent the periphery of said combustion chamber thus preventing such particles from emerging through said outlet.

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